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Z-purge Field Install

A client is proposing to retrofit a NEMA 4 pump control enclosure for use in a Class I Div 2 location by field installing a listed purge / pressurization unit from Pentair (Hoffman).

I've normally seen the purged units factory assembled in the panel shop as part of a listed industrial control panels.

Are there any issues with performing field retrofit, assuming the sizing/flowrates are properly calculated in accordance with mfr instructions? Any things to watch out for? As this is Z purge, and based on my read of NFPA 496 I think they are only required to alarm on loss of pressure, and don't need to trip the power supply to the enclosure. Is this correct?

A client is proposing to retrofit a NEMA 4 pump control enclosure for use in a Class I Div 2 location by field installing a listed purge / pressurization unit from Pentair (Hoffman).

I've normally seen the purged units factory assembled in the panel shop as part of a listed industrial control panels.

Are there any issues with performing field retrofit, assuming the sizing/flowrates are properly calculated in accordance with mfr instructions? Any things to watch out for? As this is Z purge, and based on my read of NFPA 496 I think they are only required to alarm on loss of pressure, and don't need to trip the power supply to the enclosure. Is this correct? yes

I don't see an issue. The pentair units are listed for this purpose.

Follow the instructions carefully.

Keep in mind that air is an expensive utility. you may wish to seal the conduits to avoid spending a ton of money on air.

Presumably the reason for doing this is that the area has been reclassified from non-hazardous to division 2. It might be a whole lot simpler to find a spot in a non-classified area to mount the control panel.

Keep in mind that air is an expensive utility. you may wish to seal the conduits to avoid spending a ton of money on air.

Presumably the reason for doing this is that the area has been reclassified from non-hazardous to division 2. It might be a whole lot simpler to find a spot in a non-classified area to mount the control panel.

I agree. There are no inherent problems with a field installation beyond what are already issues with a factory installation.

You hit on the major issue: "air ain't cheap." The full economics are rarely realized until well after the decision is made to go with an "active" rather than "passive" protective technique. That said, Type Z pressurizing is fairly benign. Other than insuring the air source is genuinely clean, it's relatively inexpensive. I agree that sealing the raceways is a good idea to maintain pressure. IMO the seals don't even need to be explosionproof​ which also benefits the economics.

This is a new install but field modified enclosure. My preference is to locate the box outside the haz area but that results in longer control cabling (I assume that is their reason - still trying to nail that down). I generally prefer passive protection to the active purged system.